The theme of this Program Project is the structure and function of the vitamin K-dependent factors, especially as these relate to their regulatory interactions with appropriate cofactors and cell binding proteins. The proposal is a logical extension of previous studies on the vitamin K-dependent factors. The results of the proposed project address basic questions that will ultimately be of value in understanding the pathogenesis and potential treatment of various thrombotic and hemorrhagic disorders that are a major cause of morbidity and mortality in this country. The Program Project consists of four research subprojects and two core units. In Project 1, Dr. Stafford will continue his work on the vitamin K- dependent carboxylase (VKC) (which he has recently purified and cloned), in particular the role of the propeptide and amino terminal domains of factor IX in recognition by VKC. In Project 2, Drs. Roberts and Monroe will extend their studies on the structure and function of factor IX, especially the platelet receptor for factor IX, and they will seek to establish the role, if any, of tissue factor pathway inhibitor deficiency in ameliorating hemophilia. In Project 3, Drs. Hiskey and Pedersen will employ the new technique of capillary zone electrophoresis to determine the processivity and sequence of carboxylation of glutamyl residues on factor IX, using VKC. In Project 4, Drs. Church and Hoffman will study the interaction of protein C with the thrombin receptor, thrombomodulin, and protein C inhibitor to determine how this important protein is regulated. These projects will employ state of the art techniques, including gene knockout technology, to answer questions that are interrelated. The team has worked together for many years, and represent a multidisciplinary approach to related problems, the sum of which is greater than the component parts.